13.3 Reactions of alkenes

Question 1

Are alkenes more or less reactive than alkanes

Answer 1

MUCH MORE
due to presence of the π-bond
π-electrons are more exposed than electrons in σ-bond electrons
π-bond readily breaks and alkenes undergo addition reactions

Question 2

Alkenes undergo many addition reactions for example with:

Answer 2

Hydrogen in the presence of a nickel catalyst
Halogens
Hydrogen halides
Steam in the presence of an acid catalyst

Each involves addition of small molecule across double bond causing the π-bond to break and for new bonds to form

Question 3

What is hydrogenation

Answer 3

The addition reaction in which hydrogen is added across a double bond

Question 4

What can the reaction of alkenes with bromine be used to identify

Answer 4

Identify if there is a C=C bond present and the organic compound is unsaturated

Question 5

What happens when bromine water is added dropwise to a sample of an alkene

Answer 5

Bromine adds across the double bond

Orange colour disappears indicating the presence of a C=C bond

Question 6

What happens when bromine water is added dropwise to a saturate compound

Answer 6

There is no addition reaction and no colour change

Question 7

What do alkenes react with gaseous hydrogen halides at room temperature to form

Answer 7

Haloalkanes
If alkene is a gas, then the reaction takes place when the two gases are mixed, if the alkene is a liquid, then the hydrogen halide is bubbled through it
Also react with concentrated hydrochloric or hydrobromic acid

Question 8

When are alcohols formed

Answer 8

When alkenes react with steam
Steam adds across the double bond
Used to produce ethanol from ethene
Two possible products